Wiring board comprising granular magnetic film

ABSTRACT

In order to provide a wiring board comprising a magnetic material effective in suppressing spurious radiation in semiconductor devices and electronic circuits and the like that operate at high speeds, a wiring board ( 15 ) comprises an insulative base material ( 17 ), conductor patterns ( 19   a  to  19   f ) formed thereon, and magnetic thin films ( 21   a  to  21   f ) formed on the conductor patterns ( 19   a  to  19   f ). The magnetic thin film is configured of a magnetic loss material represented by M-X—Y, where M is at least one of Fe, Co, and Ni, X is at least one element other than M or Y, and Y is at least one of F, N, and O, the maximum value μ″max of the loss factor μ″ that is an imaginary component in the complex permeability characteristic of the magnetic loss material exists within a frequency range of 100 MHz to 10 GHz, and a relative bandwidth bwr is not greater than 200% or not smaller than 150% where the relative bandwidth bwr is obtained by extracting a frequency bandwidth between two frequencies at which the value of μ″ is 50% of the maximum μ″ max  and normalizing the frequency bandwidth at the center frequency thereof.

This application is a divisional of application Ser. No. 09/825,418,filed 3 Apr. 2001 now U.S. Pat. No. 6,653,573, a Convention applicationbased on Japanese applications 101756 and 101765, both filed 4 Apr.2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to wiring boards that comprise magnetic bodiesthat exhibit outstanding magnetic loss characteristics at highfrequencies, and more particularly to wiring boards such as flexiblewiring boards and flexible flat cables that comprise multilayer orunilayer wiring boards or high-frequency current suppression bodieswherein magnetic loss materials are used that exhibit outstandingcomplex permeability characteristics and are effective in suppressingelectromagnetic interference and spurious radiation that are problematicin active devices that operate at high speed, high-frequency electroniccomponents, and electronic equipment mounted thereon.

2. Description of the Related Art

In recent years, the proliferation of highly integrated semiconductordevices has been remarkable which operate at high speed. Examplesinclude the random access memory (RAM), read only memory (ROM),microprocessor (MPU), central processing unit (CPU), image processingarithmetic logic unit (IPALU), and other logic circuit devices. In theseactive devices, higher speeds are being achieved at a prodigious rate interms of calculating speed and signal processing speed, and theelectrical signals propagated through the high-speed electronic circuitshave become a major cause of inductive and high-frequency noise becauseof the rapid voltage and current changes associated therewith.Meanwhile, the trend toward lighter weight, thinner profile, and smallersize in electronic components and electronic equipment continues rapidlyand unabatedly. In conjunction with that trend, the integration levelsbeing achieved in semiconductor devices and the higher electroniccomponent mounting densities being realized in printed wiring or circuitboards are also remarkable. Accordingly, electronic devices and signallines that are integrated or mounted overly densely become extremelyclose to each other, and the situation is now such that, in conjunctionwith the higher signal processing speeds being achieved, as remarkedearlier, high-frequency spurious radiation noise is easily induced.

Problems have been pointed out with spurious radiation from power supplylines going to active devices in such recent electronic integrateddevices and wiring boards, against which such measures as the insertionof decoupling condensers or other concentrated constant components intothe power lines have been implemented.

However, because the noise generated in higher speed implementations ofelectronic integrated devices and wiring boards contains harmoniccomponents, signal paths exhibit a distributed constant behavior, andsituations have arisen where measures against noise that presumeconventional concentrated constant circuits are ineffective.

Similar problems have arisen also, inside electronic equipment, relatingto connections between boards, and to the flexible wiring or printedcircuit boards (FPCs) or flexible flat cables (FFCs) (hereinafter bothreferred to by the generic term flexible wiring or printed circuit board(FPC)) mounted to electronic components.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide flexible wiringboards that comprise magnetic material effective in countering spuriousradiation from semiconductor devices and electronic circuits thatoperate at high speeds, as described above.

It is another object of the present invention is to provide flexiblewiring boards that comprise magnetic loss materials exhibiting a largemagnetic loss factor μ″ wherewith effective measures against spuriousradiation can be implemented with a magnetic body of smaller volume.

According to one aspect of the present invention, there is provided awiring board which comprises an insulative base material, conductorpatterns formed thereon, and magnetic thin films formed on the conductorpattern.

In the aspect of the present invention, it is preferable that themagnetic thin film is configured of a magnetic loss material having acomposition represented by M-X—Y, where M is at least one of Fe, Co, andNi, X is at least one element other than M or Y, and Y is at least oneof F, N, and O, that the magnetic loss material is a narrow-bandmagnetic loss material in which a maximum value μ″max of loss factor μ″that is imaginary component in complex permeability characteristic ofthe magnetic loss material exists within a frequency range of 100 MHz to10 GHz, and that a relative bandwidth bwr is not greater than 200% wherethe relative bandwidth bwr is obtained by extracting a frequencybandwidth between two frequencies at which the value of μ″ is 50% of themaximum μ″_(max) and normalizing the frequency bandwidth at the centerfrequency thereof.

In the aspect of the present invention, it is also preferable that themagnetic thin film is configured of a magnetic loss material having acomposition represented by M-X—Y, where M is at least one of Fe, Co, andNi, X is at least one element other than M or Y, and Y is at least oneof F, N, and O, that the magnetic loss material is a broad-band magneticloss material in which maximum value μ″max of loss factor μ″ that isimaginary component in complex permeability characteristic of themagnetic loss material exists within a frequency range of 100 MHz to 10GHz, and that a relative bandwidth bwr is not smaller than 150% wherethe relative bandwidth bwr is obtained by extracting a frequencybandwidth between two frequencies at which the value of μ″ is 50% of themaximum μ″_(max) and normalizing the frequency bandwidth at the centerfrequency thereof.

According to another aspect of the present invention, there is provideda wiring board which comprises a board of at least one layer comprisinga conductor part, and magnetic thin films deployed at least on part ofthe board or the conductor part.

In the aspect of the present invention, it is also preferable that themagnetic thin film is configured of a magnetic loss material having acomposition represented by M-X—Y, where M is at least one of Fe, Co, andNi, Y is at least one of F, N, and O, and X is at least one elementother than M or Y, the magnetic loss material is a narrow-band magneticloss material in which maximum value μ″max of loss factor μ″ that isimaginary component in complex permeability of the magnetic lossmaterial exists within a frequency range of 100 MHz to 10 GHz, and thata relative bandwidth bwr is not greater than 200% where the relativebandwidth bwr is obtained by extracting a frequency bandwidth betweentwo frequencies at which the value of μ″ is 50% of the maximum μ″_(max)and normalizing the frequency bandwidth at the center frequency thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section of a flexible wiring board according to a firstembodiment of the present invention;

FIGS. 2A to 2E are sections representing, in order, procedures forfabricating the flexible wiring board diagrammed in FIG. 1;

FIG. 3 is a section of a multilayer printed wiring board according to asecond embodiment of the present invention;

FIG. 4 is a diagram of a simplified apparatus configuration for forminga granular magnetic thin film;

FIG. 5 is a graph representing an example of the frequency dependency ofμ″ in a sample 1 according to an embodiment of the present invention;

FIG. 6 is a section of a multilayer printed wiring board according to athird embodiment of the present invention;

FIG. 7 is a section of a multilayer printed wiring board according to afourth embodiment of the present invention;

FIG. 8 is a diagram representing a simplified apparatus configurationfor forming a granular magnetic thin film;

FIG. 9 is a graph representing an example of the frequency dependency ofμ″ in a sample 2 according to an embodiment of the present invention;

FIG. 10 is a graph representing an example of the frequency dependencyof μ″ in a comparative sample 2;

FIG. 11 is a diagonal view of a measurement system for observing thesuppression effect of a high-frequency current suppression bodycomprising a magnetic loss material according to the present invention;

FIG. 12A is a graph of the transmission characteristic (S21) of sample 1according to an embodiment of the present invention;

FIG. 12B is a graph of the transmission characteristic (S21) of acomposite magnetic sheet that is a comparative sample 1;

FIG. 13 is a diagram of an equivalent circuit of a magnetic bodyaccording to an embodiment of the present invention;

FIG. 14A is a graph of the R value calculated from the transmissioncharacteristic of the sample 1, according to an embodiment of thepresent invention; and

FIG. 14B is a graph of the R value calculated from the transmissioncharacteristic of a composite magnetic sheet that is a comparativesample.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The history of the present invention will be specifically describedprior to describing embodiments of the present invention.

The inventors, having previously invented a composite magnetic bodyexhibiting large magnetic loss at high frequencies, discovered a methodwherewith, by deploying that composite magnetic body in the vicinity ofa spurious radiation source, the generation of spurious radiation fromthe semiconductor devices and electronic circuits noted earlier, etc.,is effectively suppressed. It is known from recent research on theactive mechanism of spurious radiation attenuation using such magneticloss is based on the impartation of equivalent resistance components tothe electronic circuits constituting sources of spurious radiation.Here, the size of the equivalent resistance component is dependent onthe size of the magnetic loss factor μ″ of the magnetic body. Morespecifically, the size of the resistance component that is equivalentlyinserted in an electronic circuit is roughly proportional to μ″ and thethickness of the magnetic body when the area of the magnetic body isconstant. Accordingly, a larger μ″ becomes necessary in order to obtaina desired spurious radiation attenuation with a smaller or thinnermagnetic body.

For example, in order to effect measures against spurious radiationusing a magnetic loss body in a miniscule region such as in the interiorof a semiconductor device mold, an extremely large value for themagnetic loss factor μ″ becomes necessary, whereupon magnetic bodieshaving significantly larger μ″ than conventional magnetic loss materialshave been sought.

The inventors, in the course of their research on soft magneticmaterials using a sputtering or vapor deposition method, took note ofthe outstanding permeability of granular magnetic bodies wherein veryfine magnetic metal particles are diffused uniformly in a non-magneticbody such as a ceramic, and conducted research on the microstructures ofmagnetic metal particles and the non-magnetic bodies surrounding them.As a result, the inventors discovered that outstanding magnetic losscharacteristics are obtained in high-frequency regions when theconcentration of magnetic metal particles in a granular magnetic body iswithin a certain range.

Now, much research has been done to date on granular magnetic bodieshaving M-X—Y compositions (where M is a magnetic metal element, Y iseither O, N, or F, and X is an element other than M or Y), and it isknown that these are low-loss and exhibit large saturationmagnetization. In these M-X—Y granular magnetic bodies, the size of thesaturation magnetization is dependent on the volume ratio accounted forby the M component. Therefore, the ratio of the M component must be madehigh to obtain large saturation magnetization. For that reason, theratio of the M component in an M-X—Y granular magnetic body for anordinary application such as use as a magnet core in a high-frequencyinductor device or transformer or the like has been limited to a rangewherewith a saturation magnetization of roughly 80% or greater can berealized for the saturation magnetization of the bulk metal magneticbody consisting exclusively of the M component.

The inventors studied the ratio of the M component in granular magneticbodies having the M-X—Y composition (where M is a magnetic metalelement, Y is either O, N, or F, and X is an element other than M or Y)across a wide range, and discovered, as a result, that, with everycomposition system, large magnetic loss is exhibited in high-frequencyregions when the magnetic metal M is present within a specificconcentration range.

Furthermore, the highest region where the M component exhibits asaturation magnetization of 80% or greater relative to the saturationmagnetization of a bulk metal magnetic body consisting exclusively ofthe M component is the M-X—Y granular magnetic body region of low lossat high saturation magnetization that has been widely researched forsome time. Materials in this region are used in high-frequencymicromagnetic devices such as the high-frequency inductors mentionedabove because the values of the real-part permeability (μ′) and thesaturation magnetization are both large, but the ratio accounted for bythe X—Y component that affects electrical resistance is small, whereforeelectrical resistivity is also small. For that reason, when the filmthickness becomes thin, the permeability at high frequenciesdeteriorates in conjunction with the development of eddy current loss inthe high-frequency region, wherefore these materials are unsuitable foruse in comparatively thick magnetic films such as are used to suppressnoise. In the region for the M component ratio exhibiting a saturationmagnetization of 80% or less but 60% or more of the saturationmagnetization of a bulk metal magnetic body consisting of only the Mcomponent, the electrical resistivity is comparatively large at roughly100 μΩ·cm or greater. Therefore, even if the thickness of the materialis on the order of several μm, the loss due to eddy currents is small,and almost all of the magnetic loss will be due to natural resonance.For that reason, the frequency dispersion width for the magnetic lossfactor μ″ will become narrow, wherefore such materials are suitable foranti-noise measures in narrow-band frequency ranges. Here, in the regionfor the M component ratio exhibiting a saturation magnetization that is60% or less but 35% or greater of the saturation magnetization of a bulkmetal magnetic body consisting solely of the M component, the electricalresistivity will be even larger, at roughly 500 μΩ·cm or greater, so theloss due to eddy currents will be extremely small, and, because themagnetic interaction between M component becomes small, spin thermaldisturbance becomes large, and quivering develops in the frequency wherenatural resonance occurs. As a consequence, the magnetic loss factor μ″will come to exhibit a large value across a broad range. Accordingly,this composition region is suitable for wide-band high-frequency currentsuppression.

In regions where the M component ratio is even smaller than in theregion of the present invention, on the other hand, super-normalmagnetism will occur because the magnetic interaction between Mcomponents will hardly appear at all.

When a magnetic loss material is deployed immediately adjacent to anelectronic circuit and high-frequency current is to be suppressed, thematerial design standard is given by the product of the magnetic lossfactor μ″ and the thickness δ of the magnetic loss material, that is,μ″·δ, and, in order to effectively suppress the high-frequency currentat a frequency of several hundreds of MHz, the rough requirement will beμ″·δ≧1000 (μm).

Accordingly, with a magnetic loss material exhibiting μ″=1000, athickness of 1 μm or greater becomes necessary, whereupon a material oflow electrical resistance susceptible to eddy current loss is notsuitable, but what is suitable is a composition wherewith the electricalresistivity becomes 100 μΩcm or greater, that is, in the compositionsystem of the present invention, wherein the M component ratio is in aregion where a saturation magnetization is exhibited that is 80% orlower than the saturation magnetization of a bulk metal magnetic bodyconsisting solely of the M component and super-normal magnetism is notmanifest, that is, a region exhibiting a saturation magnetization thatis 35% or greater relative to the saturation magnetization of the bulkmetal magnetic body consisting solely of the M component.

The inventors arrived at the present invention by applying such amagnetic material to flexible wiring or printed circuit boards.

Embodiments of the present invention are now described with reference tothe drawings.

Referring to FIG. 1, a flexible wiring or printed circuit board 15,which will be referred to hereinafter as flexible wiring board, has aflexible base material 17 consisting of a polyimide or the like, andconductor patterns 19 a, 19 b, 19 c, 19 d, 19 e and 19 f formed on onesurface of the base material 17. Granular magnetic thin films 21 a, 21b, 21 c, 21 d, 21 e, and 21 f are formed on the upper surfaces of theconductor patterns 19 a, 19 b, 19 c, 19 d, 19 e and 19 f so as tocoincide with each of those conductor patterns 19 a, 19 b, 19 c, 19 d,19 e, and 19 f.

Referring to FIG. 2A, a copper foil 19 is formed by rolling and isapplied across one entire surface of the flexible base material 17.Another conductive metal foil may be used instead of this copper foil19, or it may be a foil made by non-electrolytic plating andelectroplating on top thereof.

Referring to FIG. 2B, a granular magnetic thin film 21 is formed byvapor deposition so as to cover the entire surface of the copper foil19.

Next, as diagrammed in FIG. 2C, a resist material comprising aUV-hardening resin is applied on that granular magnetic thin film 21,photo-exposed to the desired pattern. The portions other than thoseexposed are removed with a solvent. As necessary, a heat treatment mayalso be performed, and the resist patterns 23 a, 23 b, 23 c, 23 d, 23 e,and 23 f hardened.

As diagrammed in FIG. 2D, the granular magnetic thin film 21 and copperfoil 19 corresponding to the portions where the resist patterns 23 a, 23b, 23 c, 23 d, 23 e, and 23 f are not formed on the upper surface aresimultaneously removed, either by soaking the board whereon the resisthas been deployed in a solution of iron chloride (III) or ferricchloride used in ordinary copper etching or similarly by spraying asolution of iron chloride (III) used in ordinary copper etching on fromthe side where the resist patterns 23 a, 23 b, 23 c, 23 d, 23 e, and 23f are present.

Conductor patterns 19 a, 19 b, 19 c, 19 d, 19 e, and 19 f are formedeach of which is covered by the granular magnetic thin films 21 a, 21 b,21 c, 21 d, 21 e, and 21 f diagrammed in FIG. 2E. In this condition,furthermore, when the resists 23 a, 23 b, 23 c, 23 d, 23 e, and 23 f areremoved, a flexible wiring board 15 such as diagrammed in FIG. 1 iscompleted.

Referring to FIG. 3, a flexible wiring board 25 according to a secondembodiment of the present invention is like a conventional flexiblewiring board in that conductor patterns 27 a, 27 b, 27 c, 27 d, and 27 eof copper or other conductive metal are deployed on the flexible basematerial 17 of a polyimide or the like.

However, in the flexible wiring board 25 according to the secondembodiment of the present invention, an insulation layer 25 is deployedwhich consists of a synthetic resin or the like so as to cover theentire surface on the side where the conductor patterns 27 a, 27 b, 27c, 27 d, and 27 e are deployed, inclusive of the conductor patterns 27a, 27 b, 27 c, 27 d, and 27 e, and on the surface of that insulationlayer 25 is formed a granular magnetic thin film 31, by vapor depositionor the like, across the entirety thereof. If necessary, moreover, suchcan be formed in one part only.

In the flexible wiring boards 15 and 25 according to the first andsecond embodiments having such configurations as these, the granularmagnetic thin film 1 absorbs electromagnetic waves that are spuriouslyemitted from the conductor patterns and converts them to heat, so thatthe emission of high-frequency noise from these flexible wiring boards15 and 25 to the outside can be suppressed.

A resin or the like other than a polyimide can be used for the basematerial of the wiring board so long as it is a synthetic resinexhibiting insulating properties and flexibility.

Next, with reference to FIG. 4, a specific example of a manufacturingmethod for the granular magnetic thin film (magnetic body M-X—Y)according to the embodiments of the present invention is described.

Referring to FIG. 4, a granular magnetic thin film manufacturingapparatus 33 comprises a vacuum chamber 35. The vacuum chamber 35comprises a vacuum pump 37 for exhausting the air, and a gas supply unit39. Inside the vacuum chamber 35 are comprised a crucible 41 and, abovethat crucible 41, a board 43. A shutter 45 is deployed between the board43 and the crucible 41.

Next, an example of manufacturing a granular magnetic thin film usingthe granular magnetic thin film vapor-deposition apparatus diagrammed inFIG. 4 is described.

(Sample 1)

A granular magnetic thin film was fabricated on a base materialconsisting of a glass board 43, by vapor deposition, under theconditions noted in Table 1 below, using the granular magnetic thin filmvapor deposition apparatus 33 diagrammed in FIG. 4, and a heat treatmentwas performed at 300° C. for 2 hours in a vacuum magnetic field to yieldsample 1.

When sample 1 so obtained was subjected to fluoroscopic x-ray analysis,the composition of the film was found to be Fe₇₂Al₁₁O₁₇.

The film thickness in sample 1 was 2.0 μm, DC resistivity was 530 μΩ·cm,the anisotropic magnetic field was Hk was 180 e (1422 A/m), Ms was 16800Gauss (1.68 T), and the relative bandwidth bwr was 148%. The relativebandwidth bwr is obtained by extracting a frequency bandwidth betweentwo frequencies at which the value of μ″ is 50% of the maximum μ″_(max)and normalizing the frequency bandwidth at the center frequency thereof.The value of the ratio between the saturation magnetization of sample 1and the saturation magnetization of a metal magnetic body consistingsolely of the M component was 72.2%.

TABLE 1 Vacuum Degree before Deposition <1 × 10⁻⁶ Torr (=1.33 × 10⁻⁴ Pa)Oxygen Flow Rate upon Deposition 3.0 sccm Material Fe₇₀Al₃₀ alloy

In order to verify the magnetic loss characteristics of the obtainedsample 1, the μ-f characteristic was investigated. Measuring the μ-fcharacteristic is done by inserting the sample into a detection coilfashioned in a rectangular shape, and measuring the impedance whileapplying a bias magnetic field. Thus the frequency characteristics ofthe magnetic loss factor μ″ are obtained.

(Comparative Sample 1)

Comparative sample 1 was obtained by the same method and under the sameconditions as sample 1 except in that the number of Al₂O₃ chips was made90.

When the comparative sample 1 so obtained was subjected to fluoroscopicx-ray analysis, the composition of the film was found to be Fe₈₆Al₆O₈.The film thickness in comparative sample 1 was 1.2 μm, the DCresistivity was 74 μΩ·cm, the anisotropic magnetic field was 22 Oe (1738A/m), and Ms was 18800 Gauss (1.88 T). The ratio between the saturationmagnetization of comparative sample 1 and the saturation magnetizationof a metal magnetic body consisting solely of the M component, that is,the value of {Ms(M-X—Y)/Ms(M)}×100, was 85.7%.

The μ″-f characteristic of sample 1 of the present invention is plottedin FIG. 5. Referring to FIG. 5, we see that the peak is very large, andthat the dispersion is sharp, with the resonant frequency high in theneighborhood of 700 MHz.

When the μ″-f characteristic of comparative sample 1 was investigated,for comparison, it was found that a large μ″ was exhibited, reflectingthe fact of the saturation magnetization Ms being large, but also thatan eddy current loss was generated together with a rise in frequency dueto the low resistance value of the sample, that, for that reason, adeterioration in the permeability or magnetic loss characteristic occursfrom the low-frequency region, and that the permeability characteristicshave become poor at high frequency.

It will be seen from these results that the magnetic body in sample 1 ofthe present invention exhibits very large magnetic loss characteristicsin the high-frequency region.

In the first and second embodiments of the present invention describedin the foregoing, moreover, an FPC board was used, but the presentinvention can also be applied besides to flexible flat cables (FFCs)having a similar configuration.

Referring to FIG. 6, a multi-layer printed wiring or interconnectionboard 51, which will be hereinafter referred to as multiplayer printedwiring board, according to a third embodiment of the present inventionhas a laminar structure wherein a first to a fifth printed wiring board53, 55, 57, 59, and 61 are stacked up. A granular magnetic thin film 65is formed across the entire surface of a ground pattern 63 deployed onone surface of the first printed wiring board 55 that consists of aglass epoxy material. A conductor pattern 67, on the other hand, isformed on the surface that is on the opposite side from the groundpattern 63 on the printed wiring board. On that conductor pattern 67,further, are formed granular magnetic thin films 65. And on thosesurfaces is formed a second printed wiring board 53 made of a glassepoxy material. This second printed wiring board 53 is essentially aninsulating board that has no conductor pattern. The second printedwiring board 53 does not have the conductor pattern 67, but has thegranular magnetic thin film 65 formed across the entire outer surfacethereof.

Meanwhile, on the one surface side of the first printed wiring board 55,the other surface of the third printed wiring board 57 comprising theconductor pattern 67 on the one surface thereof is stacked. Then, on theconductor pattern 67 of the third printed wiring board 57, the granularmagnetic thin films 65 are formed. On this third printed wiring board 57is formed the fourth printed wiring board 59 consisting of a glass epoxymaterial. On the surface of the fourth printed wiring board 59 that ison the opposite side from the third printed wiring board 57 are formedthe conductor patterns 67, and on top of that are formed the granularmagnetic thin films 65.

On the fourth printed wiring board 59 the fifth printed wiring board 61consisting of a glass epoxy material is formed. On the surface of thisfifth printed wiring board 61 that is on the opposite side from thefourth printed wiring board 57, the conductor patterns 67 are formed,and on top of those, the granular magnetic thin films 65 are formed.Further, also on the surface where no conductor patterns 67 are formed,the granular magnetic thin films 65 are formed, at intervals with theconductor patterns 67. The granular magnetic thin films 65 deployedbetween the conductor patterns can be deployed directly on theinsulation board and used as conductors even if not deployed so as tomake contact on the conductor patterns 67.

In a multi-layer wiring board according to the third embodiment havingsuch a configuration as this, the granular magnetic thin films 65 absorbthe high frequency waves emitted from the conductor patterns 67, andconvert them to heat. Therefore, the emission of high-frequency noisefrom the multi-layer wiring board to the outside can be suppressed.

The multi-layer wiring board according to the third embodiment isconfigured such that, after applying the first and third printed wiringboards 55 and 57, the second, fourth, and fifth printed wiring boards orinsulation layers are formed in order. However, it goes without sayingthat multiple printed wiring boards having a glass epoxy material as theboard may be prepared from the beginning, and those applied using anadhesive such as an epoxy resin or the like.

Polyimides and the like, for example, can also be used for the boards,so long as they are synthetic resins exhibiting insulative properties.

The granular magnetic thin film 1, moreover, can be deployed directly onthe insulation board and used as a conductor, even if not deployed onthe conductor pattern 2.

Making reference to FIG. 7, a multi-layer wiring board 69 according tothe fourth embodiment of the present invention has first to fifthprinted wiring boards 55, 53, 57, 59, and 61, having a polyimide astheir base material, formed in laminar fashion. The second printedwiring board 53 deployed below the first printed wiring board 55comprises a ground pattern 63 on one surface thereof, and a conductorpattern 67 on the other surface thereof. On the ground pattern of thesecond printed wiring board 53 is formed a granular magnetic thin film65 across the entire surface thereof. On the conductor pattern on theother surface of the second printed wiring board 53, meanwhile, granularmagnetic thin films 65 are formed, and thereupon is stacked one surfaceside of the first printed wiring board 55. On the other surface side ofthe first printed wiring board 55 are formed the third and fourthprinted wiring boards 57 and 59, each having conductor patterns 67 onone side thereof. On those conductor patterns 67 are formed granularmagnetic thin films 65.

On the surface of the fourth printed wiring board 59 on which theconductor patterns 67 are formed is formed the fifth printed wiringboard 61. An insulation film 71 is formed so as to cover the entiresurface of the surface where the conductor patterns 67 on the outersurface of the fifth printed wiring board 61 are formed, and thegranular magnetic thin film 65 is formed so as to cover the entiresurface thereon.

In the multi-layer wiring board 69 according to the second embodimenthaving such a configuration as this, the high-frequency waves emittedfrom the conductor patterns 67 are absorbed by the granular magneticthin films 65, and converted to heat, wherefore the emission ofhigh-frequency noise from the multi-layer wiring board to the outsidecan be suppressed.

This granular magnetic thin film 65 exhibits conductivity and comprisesa metal magnetic body, wherefore it can be used directly as a conductor.

The multi-layer wiring board according to the second embodiment,moreover, is configured with the first, third, fourth, and fifth printedwiring boards formed successively on the second printed wiring board 55.However, it goes without saying that multiple printed wiring boardshaving conductor patterns and using a polyimide as the board may beprepared from the beginning, and those applied similarly using anadhesive such as an epoxy resin or the like.

Next, the granular magnetic body M-X—Y structure based in being used inthe embodiments of the present invention and a specific example of amanufacturing method therefor are described next, making reference toFIG. 8.

Referring to FIG. 8, a sputtering apparatus 73 comprises a target sampletable platform 75 and board 77 inside a vacuum chamber 35 capable ofhaving the air therein exhausted by a vacuum pump 37. The target sampleplatform 75 is connected to an RF power supply 79 from the outside. Onthe target sample platform 75 are a target 81 and a tip 83 placedthereon. Between the target sample platform 75 and the board 77 isdeployed a shutter 45 so as to cover the board 77. Symbol 39 designatesa gas supply unit for supplying gas to the inside of the chamber, whilesymbol 85 designates a supporting platform for supporting the board 77.

A manufacturing example is next described.

(Sample 2)

Using the apparatus diagrammed in FIG. 8, a granular magnetic thin filmwas fabricated on the glass board 77 by sputtering, under the conditionsnoted below in Table 2. The sputtered film obtained thereby wassubjected to a heat treatment in a vacuum magnetic field for 2 hours at300° C. to yield sample 2. When this sample 2 was subjected tofluoroscopic x-ray analysis, the composition of the film was found to beFe₇₂Al₁₁O₁₇. The film thickness in sample 2 was 2.0 μm, the DCresistivity was 530 μΩ·cm, Hk was 18 Oe (1422 A/m), Ms was 16800 Gauss(1.68 T), and the relative bandwidth bwr was 148%. The value of theratio between the saturation magnetization of sample 2 and thesaturation magnetization of a metal magnetic body consisting solely ofthe M component was 72.2%.

TABLE 2 Vacuum Degree before Deposition <1 × 10⁻⁶ Torr (=1.33 × 10⁻⁴ Pa)Atmosphere upon Deposition Ar Power Supply RF Target Fe (φ 100 mm) +Al₂O₃ chip (120 pieces) (chip size: 5 mm × 5 mm × 2 mmt)

In order to verify the magnetic loss characteristics of the sample, theμ-f characteristic was investigated. Measuring the μ-f characteristic isdone by inserting the sample into a detection coil fashioned in arectangular shape, and measuring the impedance while applying a biasmagnetic field. Thus the frequency characteristics of the magnetic lossfactor μ″ are obtained.

(Comparative Sample 2)

Comparative sample 2 was obtained by the same method and under the sameconditions as sample 2 except in that the number of Al₂O₃ chips was made90.

When the comparative sample 2 so obtained was subjected to fluoroscopicx-ray analysis, the composition of the film was found to be Fe₈₆Al₆O₈.The film thickness was 1.2 μm, the DC resistivity in comparative sample2 was 74 μΩ·cm, the anisotropic magnetic field was 22 Oe (1738 A/m), andMs was 18800 Gauss (1.88 T). The ratio between the saturationmagnetization of comparative sample 2 and the saturation magnetizationof a metal magnetic body consisting solely of the M component, that is,the value of {Ms(M-X—Y)/Ms(M)}×100, was 85.7%.

Referring to FIG. 9, in the μ″-f characteristic of sample 2 of thepresent invention, the peak is very high, and the dispersion is sharp,with the resonant frequency high in the neighborhood of 700 MHz.

Referring to FIG. 10, in the μ″-f characteristic, comparative sample 2exhibits a large μ″, reflecting the fact that the saturationmagnetization Ms is large. However, because the resistance value ofcomparative sample 2 is low, eddy current losses are generated as thefrequency rises. Thus it is evident that a deterioration in thepermeability (magnetic loss characteristic) has developed from thelow-frequency region, and that the permeability characteristics havebecome poor at high frequencies.

It will be seen from these results that the magnetic body in sample 2 ofthe present invention exhibits very high magnetic loss characteristicsin high-frequency regions.

Next are described tests done to verify noise suppression effectivenessusing samples 1 and 2 obtained with the embodiments of the presentinvention. These tests were identical for samples 1 and 2, whereforeonly the tests for sample 1 are described.

Using the measurement system 91 diagrammed in FIG. 11 to verify noisesuppression effectiveness, and using an electromagnetic interferencesuppressing body comprising sample 1 of a granular magnetic thin filmhaving the permeability characteristic diagrammed in FIG. 5, formed in asquare 20 mm on a side, with a film thickness of 2.0 μm, that was placeddirectly above a microstrip line having a line length of 75 mm and acharacteristic impedance of 50 Ω, and the transmission characteristicsbetween 2 Ports were determined using a network analyzer (HP 8753D).Symbol 93 designates a coaxial line connecting the microstrip line andthe network analyzer. The results are given in Table 3 below.

TABLE 3 Permeability Characteristics Granular Magnetic Composite ThinFilm Magnetic Sheet μ ″/700 MHz about 1800 about 3.0 bwr (%) 148 196

In Table 3 above, the permeability characteristics for theelectromagnetic interference suppression sheet of the granular magneticthin film sample 1 are given together with the characteristics for acomposite magnetic sheet of the same area consisting of flat Sendustpowder and a polymer used as a comparative sample. The μ″ of thegranular magnetic thin film sample 1 exhibits a dispersion in thesub-microwave band, with a size μ″max=approximately 1800 in the vicinityof 700 MHz. This is some 600 times larger than the μ″ of the comparativesample that exhibits μ″ dispersion in the same band. Furthermore, therelative bandwidth bwr is small as compared with that of the comparativesample. When high-frequency currents are suppressed by deploying amagnetic loss material immediately next to a noise transmission path andimparting an equivalent resistance component to the transmission path,it is believed that the level of suppression effect will be roughlyproportional to the product of the size of μ″ and the thickness of themagnetic body (μ″·δ) wherefore, when comparing suppression effects, acomposite magnetic sheet wherein δ=1.0 mm at μ″≈3 such that the value ofμ″·δ will be on the same order was used as the comparative example.

More specifically, as diagrammed in FIG. 11, an electromagneticinterference suppression body sheet 89 was deployed directly over amicrostrip line 87 as indicated by the dotted line 89′, and the changesin the transmission characteristic S₂₁ was determined. In FIGS. 12A and12B, the S₂₁ characteristics are plotted when deploying, respectively,the electromagnetic interference suppression body sheet of the granularmagnetic thin film sample 1 and the composite magnetic sheet. With thedeployment of the granular magnetic thin film sample 1, the S₂₁characteristic decreases at and above 100 MHz, then increases afterexhibiting an extremely small value of −10 dB near 2 GHz. In the case ofthe composite magnetic sheet, on the other hand, the S₂₁ characteristicsimply decreases from several hundreds of MHz on, exhibitingapproximately −10 dB at 3 GHz. These results indicate both that the S₂₁transmission characteristic is dependent on the μ″ dispersion of themagnetic body, and that the level of the suppression effect is dependenton the μ″·δ product. Thereupon, the magnetic body was assumed to be adimension λ distribution constant line such as diagrammed in FIG. 13,and, after finding the equivalent circuit constant per unit length (Δλ)from the transmission characteristics S₁₁ and S₂₁, the equivalentcircuit constant converted to the sample dimension (λ) was calculated.When a magnetic body is placed above a microstrip line, as in thisstudy, because the changes in transmission characteristic are mainly dueto the equivalent resistance component that is added in series, theequivalent resistance R was found, and the frequency dependency thereofwas investigated. In FIGS. 14A and 14B, the frequency variation in theequivalent resistance R in the present invention and in the compositemagnetic sheet that is the comparative sample are plotted. In bothcases, the equivalent resistance R simply increases in the sub-microwaveband, becoming several tens of Ω at 3 GHz. The frequency dependency ofthe equivalent resistance R appears to have a different trend from thatof the frequency dispersion of μ″ that becomes extremely large in thevicinity of 1 GHz, in both cases, but this is thought to be a result ofreflecting the fact that, in addition to the μ″·δ product noted earlier,the ratio of the sample dimensions to the wavelength increases simply.

In the embodiments of the present invention, manufacturing examples areindicated that are based on sputtering or vacuum vapor depositionprocedures, but such manufacturing methods as ion beam vapor depositionor gas deposition may also be used, and there is no limit on the methodso long as it is one wherewith the magnetic loss material of the presentinvention can be uniformly effected.

In the embodiments of the present invention, moreover, it is anas-deposition film, but the performance and characteristics can beenhanced after film fabrication by performing a heat treatment in avacuum magnetic field.

Based on the foregoing, it is evident that the samples of the presentinvention that exhibit μ″ dispersion in the sub-microwave band exhibit ahigh-frequency current suppression effect equivalent to that of acomposite magnetic sheet having a thickness that is approximately 500times greater, and that such are promising as materials used to minimizeEMI, between electronic components comprising semiconductor integrateddevices and the like that operate with a high-speed clock running near 1GHz and electronic components mutually susceptible to interference, andin electronic components and circuit devices and the like that use highfrequencies.

The granular magnetic films described in the foregoing relate only toFe₈₆Al₆O₈, but it is evident that the granular magnetic thin film of thepresent invention can elicit the same effects even if, instead thereof,the components of the magnetic body with the general formula M-X—Y aresuch that M is Ni, Fe, or Co, the X component is C, B, Si, Al, Mg, Ti,Zn, Hf, Sr, Nb, Ta, or a rare earth, or, alternatively, a mixture ofthose, and the Y component is F, N, or O, or, alternatively, a mixtureof those.

The film forming method used in the embodiments described in theforegoing was sputtering, but other methods such as vapor deposition orthe like can also be employed. In addition, such manufacturing methodsas ion beam deposition or gas deposition may also be used. There is nolimitation on the method so long as it is one wherewith the granularmagnetic thin film of the present invention can be realized uniformly.

Based on the present invention, as described in the foregoing, wiringboards can be provided that have magnetic thin films which exhibitoutstanding high-frequency magnetic loss characteristics that areextremely useful in eliminating interference caused by spuriouselectromagnetic emissions or electromagnetic noise in flexible wiringboards that use high frequencies.

Based on the present invention, furthermore, unilayer or multilayerwiring boards can be provided that have magnetic thin films whichexhibit outstanding high-frequency magnetic loss characteristics thatare extremely useful in eliminating interference caused by spuriouselectromagnetic emissions or electromagnetic noise in unilayer ormultilayer wiring boards that use high frequencies.

1. A wiring board, comprising: a board of at least one layer comprisinga conductor part, said conductor part comprising-signal line conductorpatterns and having a ground part that is either a ground surface or hasground patterns deployed on one surface of said board, an entire surfaceof said ground part being covered with a magnetic thin film, whereinsaid magnetic thin film is configured of a magnetic loss materialrepresented by M-X—Y, where M is at least one of Fe, Co, and Ni, Y is atleast one of F, N, and O, and X is at least one element other than M orY, said magnetic loss material has a maximum value μ″_(max) of lossfactor μ″ that is imaginary component in complex permeability of saidmagnetic loss material existing within a frequency range of 100 MHz to10 GHz; said magnetic loss material is a broad-band magnetic lossmaterial having a relative bandwidth bwr not smaller than 150% where therelative bandwidth bwr obtained by extracting a frequency bandwidthbetween two frequencies at which the value of μ″ is 50% of the maximumμ″_(max) and normalizing the frequency bandwidth at the center frequencythereof; and said magnetic thin film deployed at least on part of saidboard or said conductor part.
 2. The wiring board according to claim 1,wherein said magnetic thin film is formed on said signal line conductorpatterns.
 3. The wiring board according to claim 1, wherein saidmagnetic thin films are formed so as to be separated from signal lineconductor patterns in portion where said signal line conductor patternsare not formed.
 4. The wiring board according to claim 1, wherein saidmagnetic thin film is deployed within insulation layer interposedtherebetween so as to cover said conductor patterns.
 5. The wiring boardaccording to claim 1, wherein said magnetic thin film is fabricated byat least one method of sputtering and vapor deposition.
 6. The wiringboard according to claim 1, wherein said magnetic thin film has athickness within a range of 0.3 μm to 20 μm.
 7. The wiring boardaccording to claim 1, wherein said wiring board is a multilayer printedwiring board comprising a structure of at least 3 layers.
 8. The wiringboard according to claim 1, wherein size of saturation magnetization insaid magnetic loss material is within a range of 60% to 35% ofsaturation magnetization of a metal magnetic body consisting solely of Mcomponent.
 9. The wiring board according to claim 1, wherein saidmagnetic loss material exhibits a DC electrical resistivity having avalue larger than 500 μΩ·cm.
 10. A wiring board, comprising: a board ofat least one layer comprising a conductor part, said conductor partcomprising signal line conductor patterns and having a ground part thatis either a ground surface or has ground patterns deployed on onesurface of said board, an entire surface of said ground part beingcovered with a magnetic thin film, wherein said magnetic thin film isconfigured of a magnetic loss material represented by M-X—Y, where M isat least one of Fe, Co, and Ni, Y is at least one of F, N, and O, and Xis at least one element other than M or Y, said magnetic loss materialhas a maximum value μ″_(max) of loss factor μ″ that is imaginarycomponent in complex permeability of said magnetic loss materialexisting within a frequency range of 100 MHz to 10 GHz; and wherein saidmagnetic loss material is a narrow band magnetic loss material having arelative bandwidth bwr not greater than 200% where the relativebandwidth bwr is obtained by extracting a frequency bandwidth betweentwo frequencies at which the value of μ″ is 50% of the maximum μ″_(max)and normalizing the frequency bandwidth at the center frequency thereof.11. The wiring board according to claim 10, wherein size of saturationmagnetization in said magnetic loss material is within a range of 80% to60% of saturation magnetization of a metal magnetic body consistingsolely of M component.
 12. The wiring board according to claim 10,wherein said magnetic loss material exhibits a DC electrical resistivitythat is within a range of 100 μΩ·cm to 700 μΩ·cm.
 13. The wiring boardaccording to claim 10, wherein X component of said magnetic thin film isat least one of C, B, Si, Al, Mg, Ti, Zn, Hf, Sr, Nb, Ta, and rare earthelements.
 14. The wiring board according to claim 10, wherein, in saidmagnetic loss material, said M exists in a granular form dispersed inmatrix of said X—Y compound.
 15. The wiring board according to claim 14,wherein mean particle diameter of particles M having said granular formis within range of 1 nm to 40 nm.
 16. The wiring board according toclaim 10, wherein said magnetic loss material exhibits an anisotropicmagnetic field Hk of 600 Oe (5.34×10⁴ A/m) or less.
 17. The wiring boardaccording to claim 10, wherein said magnetic loss material is selectedfrom Fe_(α)Al_(β)O_(γ) and Fe_(α)Si_(β)O_(γ).